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Wine is widely consumed throughout the world and represents a significant financial market, but production faces increasing challenges. While consumers progressively value more complex flavor profiles, regional authenticity, and decreased use of additives, winemakers strive for consistency among climate change, characterized by rising environmental temperatures and sun burn events. This often leads to grapes reaching phenolic maturity with higher sugar levels, and increased microbial spoilage risk.Herein, we addressed these dual concerns by investigating the use of autochthonous Saccharomyces cerevisiae strains for fermentations of grape musts resulting from these altered conditions. We characterized underexplored repositories of naturally-occurring strains isolated from different environments and geographical regions, regarding adequate enological properties (e.g., high cell growth, reduced production of H2S, ethanol and acetic acid, increased SO2 resistance, killer activity), and other less frequently investigated properties (resistance to osmotic stress, potassium and aluminium silicates and fungicides). The phenotypic data were organized in a biobank, and bioinformatic analysis grouped the strains according to their characteristics. Furthermore, we analyzed the potential of four Portuguese isolates to be used in fermentations of grape musts with high sugar levels, uncovering promising candidates. This research therefore contributes to ongoing efforts to increase sustainability and quality of wine production.

Acetic acid bacteria (AAB) are ubiquitous wine spoilage microorganisms causing significant economic damage to winemakers. Considering difficulties in their isolation through traditional microbiological methods, it would be advantageous to detect them using molecular methods at all stages of winemaking and, thus, prevent wine spoilage. In this research, we analyzed wines, musts and grapes of 13 varieties grown in different regions of the Republic of Moldova. The DNA was extracted and analyzed via PCR using home-designed primers to detect Acetobacter aceti and Acetobacter pasteurianus. Generally, samples with no detectable amounts of AAB in either musts or wine had volatile acidity within the acceptable limits. Only one grape (Rara Neagra) had detectable amounts of AAB (A. pasteurianus) at all analyzed stages (grape, must, wine), and this sample had the highest amount of volatile acidity (2.11 g/L), exceeding the maximum acceptable limit for red wines of 1.2 g/L. A. pasteurianus was more common than A. aceti, both in musts and wines. Samples positive for AAB but containing low amounts of them in wine (Cq value > 35) did not have volatile acidity above the acceptable level. Samples that were wine-negative but must-positive for AAB had volatile acidity close to the acceptable limit. This study shows the utility of PCR diagnostics for predicting the risks of wine spoilage by AAB. [ABSTRACT FROM AUTHOR]

Fumaric acid (FH2) is an additive allowed by the Codex Alimentarius and the International Organization of Vine and Wine (OIV) that can be used for wine acidification but also to inhibit malolactic fermentation (MLF). FH2 has a positive effect in the reduction in SO2 doses by controlling LAB and other bacteria and by preserving molecular SO2 due to pH effect. This article reports the use of FH2 at 600 mg/L in wines produced with 3 varieties of Vitis vinifera L. grapes (Tempranillo, Garnacha and Viura) made in vintages 2018, 2020 and 2021. Wines treated with 600 mg/L of FH2 were more stable in the long term and showed lower pH by the preservation of malic acid due to both the absence of MLF (which reduced the pH in 0.1–0.2 units compared with controls) and the effect of FH2 acidification (what produced and additional reduction of 0.05–0.1 pH units). The wines treated with FH2 also remained with very low volatile acidity contents close to 0.2 mg/L or lower. These results corroborate that FH2 can be used to successfully control malolactic fermentation in all still wine types (red, white, and rose) from either of the studied varieties. [ABSTRACT FROM AUTHOR]

Acetic acid bacteria (AAB) are ubiquitous wine spoilage microorganisms causing significant economic damage to winemakers. Considering difficulties in their isolation through traditional microbiological methods, it would be advantageous to detect them using molecular methods at all stages of winemaking and, thus, prevent wine spoilage. In this research, we analyzed wines, musts and grapes of 13 varieties grown in different regions of the Republic of Moldova. The DNA was extracted and analyzed via PCR using home-designed primers to detect Acetobacter aceti and Acetobacter pasteurianus. Generally, samples with no detectable amounts of AAB in either musts or wine had volatile acidity within the acceptable limits. Only one grape (Rara Neagra) had detectable amounts of AAB (A. pasteurianus) at all analyzed stages (grape, must, wine), and this sample had the highest amount of volatile acidity (2.11 g/L), exceeding the maximum acceptable limit for red wines of 1.2 g/L. A. pasteurianus was more common than A. aceti, both in musts and wines. Samples positive for AAB but containing low amounts of them in wine (Cq value > 35) did not have volatile acidity above the acceptable level. Samples that were wine-negative but must-positive for AAB had volatile acidity close to the acceptable limit. This study shows the utility of PCR diagnostics for predicting the risks of wine spoilage by AAB.

Wine is widely consumed throughout the world and represents a significant financial market, but production faces increasing challenges. While consumers progressively value more complex flavor profiles, regional authenticity, and decreased use of additives, winemakers strive for consistency among climate change, characterized by rising environmental temperatures and sun burn events. This often leads to grapes reaching phenolic maturity with higher sugar levels, and increased microbial spoilage risk. Herein, we addressed these dual concerns by investigating the use of autochthonous Saccharomyces cerevisiae strains for fermentations of grape musts resulting from these altered conditions. We characterized underexplored repositories of naturally-occurring strains isolated from different environments and geographical regions, regarding adequate enological properties (e.g., high cell growth, reduced production of H 2 S, ethanol and acetic acid, increased SO 2 resistance, killer activity), and other less frequently investigated properties (resistance to osmotic stress, potassium and aluminium silicates and fungicides). The phenotypic data were organized in a biobank, and bioinformatic analysis grouped the strains according to their characteristics. Furthermore, we analyzed the potential of four Portuguese isolates to be used in fermentations of grape musts with high sugar levels, uncovering promising candidates. This research therefore contributes to ongoing efforts to increase sustainability and quality of wine production., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Published by Elsevier Ltd.)

Fumaric acid (FH2) is an additive allowed by the Codex Alimentarius and the International Organization of Vine and Wine (OIV) that can be used for wine acidification but also to inhibit malolactic fermentation (MLF). FH2 has a positive effect in the reduction in SO2 doses by controlling LAB and other bacteria and by preserving molecular SO2 due to pH effect. This article reports the use of FH2 at 600 mg/L in wines produced with 3 varieties of Vitis vinifera L. grapes (Tempranillo, Garnacha and Viura) made in vintages 2018, 2020 and 2021. Wines treated with 600 mg/L of FH2 were more stable in the long term and showed lower pH by the preservation of malic acid due to both the absence of MLF (which reduced the pH in 0.1–0.2 units compared with controls) and the effect of FH2 acidification (what produced and additional reduction of 0.05–0.1 pH units). The wines treated with FH2 also remained with very low volatile acidity contents close to 0.2 mg/L or lower. These results corroborate that FH2 can be used to successfully control malolactic fermentation in all still wine types (red, white, and rose) from either of the studied varieties.

The impact of summer canopy management was investigated in Vitis vinifera L., cv. Riesling. Sugar and organic acid concentrations were measured for the six defoliation treatments. Titratable acidity (TA) was measured twice before harvest and once at the date of harvest. The same measurements were done twice during wine ageing. The young wine was measured for concentrations of malic, tartaric and volatile acids. Treatments with appropriate defoliation, where shortened lateral shoots (up to two leaves) were retained, supported the process of wine grape ripening to the greatest extend in the cool climate of the Czech Republic, while treatments with almost no defoliation yielded the worst results. The TA decreased during fruit ripening after veraison and continued to decrease during wine maturation. The tendency of decreasing with time was shown for the malic to tartaric acid ratio as well. Concentrations of volatile acids were sufficiently low in each of the treatments.

Wine is a special product with a long tradition but it is also strongly influenced by the local soil and climatic conditions of the area where the vineyards are grown, yielding the grapes from which wine is produced.Existing Greek and EU legislation has established a framework of analysis, applied on a sampling basis, with the primary aim of protecting both the consumer and the producers, by safeguarding the wine production process in accordance with scientific principles and current legislation. In the present monograph the available data from analyses carried out on samples from wines produced in Eastern Macedonia and Thrace (located in northern Greece) have been recorded, codified, quoted and processed by the relevant competent authorities of the state, using the sampling procedure provided. The work first analyzes the results produced by the analyses, in order to draw the initial conclusions. The results are then processed using an application for geographical separation, co-variance analysis for the dependent variables, and the creation of time series diagrams. The last two statistical analyses are conducted by exploiting the available climatic parameters of the area. This work has shown the high quality of the wines in the area, the general absence of problems in the wines it produces, and the respect paid to the existing legislation related to winemaking and the use of Protected Geographical Indication (PGI) provisions, since the vast majority of wines produced in the area fall into this category. The statistical analysis of the three methods used yielded indications concerning the separation of wines produced in individual areas, as well as the correlation of wine parameters with climate parameters, and the boundaries of the climatic data where the wine parameters are maximized or minimized. The results are of particular importance in the design of new vineyard installations and wineries, as well as for new wines on the one hand, and the high importance for assessing the impact of the ongoing global changes in climatic conditions on the other. At the same time, these analyses form the basis for further scientific research in order to formulate a modern, efficient, sustainable and developmental policy that includes planning for the development of viticulture and winemaking in the area, and by extension, in any other viticultural area. [ABSTRACT FROM AUTHOR]

Sour rot is a disease complex that causes serious damage in viticulture. The common vinegar fly Drosophila melanogaster (Diptera: Drosophilidae) is associated with sour rot in overripe or otherwise damaged grapes. Drosophila suzukii (Diptera: Drosophilidae) is an invasive species, which is suspected to induce sour rot in previously undamaged grapes due to the flies' ability to infest healthy, undamaged soft fruits with its serrated ovipositor. As a consequence, infection of healthy grapes by D. suzukii may facilitate the colonization by D. melanogaster. We investigated the single and combined effects of D. suzukii and D. melanogaster on sour rot development by measuring volatile acidity under near‐natural conditions in the vineyard, along with laboratory experiments under controlled climate. In 2017, the combined field and laboratory experiments suggested that the presence of D. suzukii and D. melanogaster increased the volatile acidity levels at a similar rate. In 2018, the field experiments showed an only marginal increase in sour rot development in treatments with both Drosophila species. Under more favourable laboratory conditions, the presence of D. suzukii, but not D. melanogaster triggered sour rot emergence. A facilitating effect of D. suzukii infestation for D. melanogaster was not detectable. These findings suggest that D. suzukii does in fact have the potential to trigger sour rot, but will probably rarely do so under field conditions in the vineyard, at least in the studied region. Instead, our study showed that D. melanogaster can have a similar impact on sour rot development as D. suzukii, emphasizing the need of comparative studies. [ABSTRACT FROM AUTHOR]

Off-flavors produced by undesirable microbial spoilage are a major concern in wineries, as they affect wine quality. This situation is worse in warm areas affected by global warming because of the resulting higher pHs in wines. Natural biotechnologies can aid in effectively controlling these processes, while reducing the use of chemical preservatives such as SO2. Bioacidification reduces the development of spoilage yeasts and bacteria, but also increases the amount of molecular SO2, which allows for lower total levels. The use of non-Saccharomyces yeasts, such as Lachancea thermotolerans, results in effective acidification through the production of lactic acid from sugars. Furthermore, high lactic acid contents (>4 g/L) inhibit lactic acid bacteria and have some effect on Brettanomyces. Additionally, the use of yeasts with hydroxycinnamate decarboxylase (HCDC) activity can be useful to promote the fermentative formation of stable vinylphenolic pyranoanthocyanins, reducing the amount of ethylphenol precursors. This biotechnology increases the amount of stable pigments and simultaneously prevents the formation of high contents of ethylphenols, even when the wine is contaminated by Brettanomyces.

Madeira wine is an internationally recognized fortified wine, characterized by a complex flavour and high longevity. Little is known about the impact of volatile acidity in its features along ageing. Thus, this work studied the evolution of acetic acid and ethyl acetate (volatile acidity main contributors) during the ageing processes used in Madeira wine production, canteiro and estufagem. Wines aged in canteiro for 6 up to 45 years were also evaluated. The odour rejection thresholds (ORT) were assessed in sweet (Malvasia) and dry (Sercial) wines with 5 and 10 years old, by a regular consumer panel and a non-regular consumer panel. The results showed that the formation trend of acetic acid and ethyl acetate is similar in both ageing processes and is favoured by the ageing, mostly in sweet wines. The ORT of ethyl acetate was in average 328 mg/L for both panels, while for acetic acid ranged between 1.96 and 5.72 g/L, depending on the evaluation panel and also on the age and sweetness degree of the Madeira wine. The ORT values expressed in volatile acidity ranged between 1.4 and 3.5 g/L, which are higher than the legal limits. The study pointed out that the olfactory perception of acetic acid and ethyl acetate in Madeira wines depends on their age and sweetness degree.

[GAR+] prion-like elements partially relieve carbon catabolite repression in Saccharomyces cerevisiae. They have been hypothesized to contribute to wine yeast survival and alcohol level reduction, as well as communication with bacteria and stuck fermentation. In this work, we selected [GAR+] derivatives from several genetic backgrounds. They were characterized for phenotypic penetrance, heritability and confirmed as prion-like through curing by desiccation. In terms of fermentation kinetics, the impact of the prion on anaerobic wine fermentation (natural grape juice) was either neutral or negative, depending on the genetic background. Likewise, residual sugars were higher or similar for [GAR+] as compared to the cognate [gar-] strains. The prions had little or no impact on glycerol and ethanol yields; while acetic acid yields experienced the highest variations between [GAR+] and [gar-] strains. Strains analyzed under aerobic conditions followed the same pattern, with either little or no impact on fermentation kinetics, ethanol or glycerol yield; and a clearer influence on volatile acidity. Although no clear winemaking advantages were found for [GAR+] strains in this work, they might eventually show interest for some combinations of genetic background or winemaking conditions, e.g., for reducing acetic acid yield under aerated fermentation.

In recent years, in line with consumer preferences and due to the effects of global climate change, new trends have emerged in wine fermentation and wine technology. Consumers are looking for wines with less ethanol and fruitier aromas, but also with a good balance in terms of acidity and mouthfeel. Nonconventional yeasts contain a wide range of different genera of non-Saccharomyces. If in the past they were considered spoilage yeasts, now they are used to enhance the aroma profile of wine or to modulate wine composition. Recent publications highlight the role of non-Saccharomyces as selected strains for controlling fermentations mostly in cofermentation with Saccharomyces. In this article, I have reviewed the ability of some bacteria and non-Saccharomyces strains to modulate wine acidity. [ABSTRACT FROM AUTHOR]

One interesting strategy to address the increasing alcohol content of wines, associated with climate change, is to reduce the ethanol yield during fermentation. Within this strategy, the approach that would allow the clearest reduction in alcohol content is the respiration of part of the grape sugars by yeasts. Non- Saccharomyces species can be used for this purpose but suffer from a limited ability to dominate the process and complete fermentation. In turn, Saccharomyces cerevisiae shows a high production of acetic acid under the growth conditions required for respiration. Previously proposed procedures used combinations of non- Saccharomyces and S. cerevisiae starters, or a strain of S. cerevisiae (PR1018), with unique metabolic properties. In both cases, precise management of oxygen availability was required to overcome the acetic acid problem. In this work, we have developed a laboratory scale process to take advantage of the properties of PR1018 and a strain of Metschnikowia pulcherrima. This process is more robust than the previous ones and does not rely on strict control of oxygenation or even the use of this particular strain of S. cerevisiae. Aeration can be interrupted instantly without impairing the volatile acidity. Under the selected conditions, an ethanol reduction of around 3% (v/v) was obtained compared to the standard fermentation control. • Aerobic fermentation with selected strains of M. pulcherrima and S. cerevisiae. • Low alcohol-low volatile acidity wines. • Adjusted proportion of inocula and air flow rate. • Post-aeration nitrogen nutrition impacts on alcohol levels and volatile profile. [ABSTRACT FROM AUTHOR]

The use of yeast respiratory metabolism has been proposed as a promising approach to solve the problem of increasing ethanol content in wine, which is largely due to climate change. The use of S. cerevisiae for this purpose is mostly hampered by acetic acid overproduction generated under the necessary aerobic conditions. However, it was previously shown that a reg1 mutant, alleviated for carbon catabolite repression (CCR), showed low acetic acid production under aerobic conditions. In this work directed evolution of three wine yeast strains was performed to recover CCR-alleviated strains, expecting they will also be improved concerning volatile acidity. This was done by subculturing strains on galactose, in the presence of 2-deoxyglucose for around 140 generations. As expected, all evolved yeast populations released less acetic acid than their parental strains in grape juice, under aerobic conditions. Single clones were isolated from the evolved populations, either directly or after one cycle of aerobic fermentation. Only some clones from one of three original strains showed lower acetic acid production than their parental strain. Most clones isolated from EC1118 showed slower growth. However, even the most promising clones failed to reduce acetic acid production under aerobic conditions in bioreactors. Therefore, despite the concept of selecting low acetic acid producers by using 2-deoxyglucose as selective agent was found to be correct, especially at the population level, the recovery of strains with potential industrial utility by this experimental approach remains a challenge. • Directed evolution of S. cerevisiae wine strains on galactose with 2-deoxyglucose. • All evolved cultures showed lower acetic acid yield than parental strains. • Selected clones show lower acetic acid yield than parental strain in shake flasks. • None of the selected clones retained the phenotype of interest in bioreactors. [ABSTRACT FROM AUTHOR]

The impact of summer canopy management was investigated in Vitis vinifera L., cv. Riesling. Sugar and organic acid concentrations were measured for the six defoliation treatments. Titratable acidity (TA) was measured twice before harvest and once at the date of harvest. The same measurements were done twice during wine ageing. The young wine was measured for concentrations of malic, tartaric and volatile acids. Treatments with appropriate defoliation, where shortened lateral shoots (up to two leaves) were retained, supported the process of wine grape ripening to the greatest extend in the cool climate of the Czech Republic, while treatments with almost no defoliation yielded the worst results. The TA decreased during fruit ripening after veraison and continued to decrease during wine maturation. The tendency of decreasing with time was shown for the malic to tartaric acid ratio as well. Concentrations of volatile acids were sufficiently low in each of the treatments. [ABSTRACT FROM AUTHOR]

To improve the quality of fermented drinks, or more specifically, wine, some strains of yeast have been isolated, tested and studied, such as Saccharomyces and non-Saccharomyces. Some non-conventional yeasts present good fermentative capacities and are able to ferment in quite undesirable conditions, such as the case of must, or wines that have a high concentration of acetic acid. One of those yeasts is Lachancea thermotolerants (L. thermotolerans), which has been studied for its use in wine due to its ability to decrease pH through L-lactic acid production, giving the wines a pleasant acidity. This review focuses on the recent discovery of an interesting feature of L. thermotolerans-namely, its ability to decrease wines' volatile acidity. [ABSTRACT FROM AUTHOR]

In recent years, in line with consumer preferences and due to the effects of global climate change, new trends have emerged in wine fermentation and wine technology. Consumers are looking for wines with less ethanol and fruitier aromas, but also with a good balance in terms of acidity and mouthfeel. Nonconventional yeasts contain a wide range of different genera of non-Saccharomyces. If in the past they were considered spoilage yeasts, now they are used to enhance the aroma profile of wine or to modulate wine composition. Recent publications highlight the role of non-Saccharomyces as selected strains for controlling fermentations mostly in cofermentation with Saccharomyces. In this article, I have reviewed the ability of some bacteria and non-Saccharomyces strains to modulate wine acidity.

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[Display omitted] • A low-cost digital image method was proposed to determine volatile acidity in cachaça. • A smartphone was used as a detector. • It is a tool for quality control, especially for the producers with limited resources. • The method can be easily disseminated in the manufacture environment. The present study reports the development and application of a novel method for the colorimetric determination of volatile acidity in cachaça using digital image. Cachaça is the most widely consumed beverage in Brazil and the development of efficient techniques for the determination of volatile acidity in this beverage is essentially important because this parameter directly reflects on the flavor and aroma of the drink. The method employed was digital image-based (DIB); this method involves the use of methyl orange as an indicator and the analysis of images captured and processed by a smartphone with a free application. A simple pretreatment of the samples employing a steam-dragging distillation for the extraction of volatile acids was performed before DIB analysis. The calibration curve related to anhydrous alcohol was found to be linear in the range of 25 to 275 mg/100 mL with an adjusted-R2 = 0.9912 and limit of detection of 6.70 mg/100 mL based on acetic acid content. The recovery assays conducted yielded recoveries ranging from 89.5 and 112 %. The technique proposed in this study is an easy, inexpensive and rapid tool for the quality control of cachaça , especially for small producers of the beverage who have limited financial resources. Moreover, this method is applicable to in situ analysis allowing to measure this parameter along the cachaça are produced being useful to monitor the volatile acidity. [ABSTRACT FROM AUTHOR]

To improve the quality of fermented drinks, or more specifically, wine, some strains of yeast have been isolated, tested and studied, such as Saccharomyces and non-Saccharomyces. Some non-conventional yeasts present good fermentative capacities and are able to ferment in quite undesirable conditions, such as the case of must, or wines that have a high concentration of acetic acid. One of those yeasts is Lachancea thermotolerants (L. thermotolerans), which has been studied for its use in wine due to its ability to decrease pH through L-lactic acid production, giving the wines a pleasant acidity. This review focuses on the recent discovery of an interesting feature of L. thermotolerans—namely, its ability to decrease wines’ volatile acidity.

The present study investigated chemical and sensory properties of Malvasia delle Lipari DOC (Denomination of Controlled Origin) wine fermented with a cryotolerant strain of Saccharomyces uvarum, characterized by low levels of acetic acid production. In particular, experimental wine was tested for volatile acidity and for aromatic profile by gas chromatography and the results were compared with the same wine produced with a commercial strain of Saccharomyces cerevisiae. Sensory analysis was carried out to assess the identification of experimental wine as Malvasia delle Lipari by defining its sensory profile. Fermentation with S. uvarum gave a final product with lower volatile acidity, lower alcohol content and higher total acidity. Moreover, differences in the aroma profile could be ascribed to different characteristics of the yeasts. Concerning sensorial analysis, the panel assigned higher scores in positive attributes to the wine fermented with S. uvarum.

Background: Aerobic fermentation of grape must, leading to respiro-fermentative metabolism of sugars, has been proposed as way of reducing alcohol content in wines. Two factors limit the usefulness of Saccharomyces cerevisiae for this application, the Crabtree effect, and excess volatile acidity under aerobic conditions. This work aimed to explore the impact on ethanol acetate production of different S. cerevisiae strains deleted for genes previously related with the Crabtree phenotype. Results: Recombinant strains were constructed on a wine industrial genetic background, FX10. All yeast strains, including FX10, showed respiro-fermentative metabolism in natural grape must under aerobic conditions, as well as a concomitant reduction in ethanol yield. This indicates that the Crabtree effect is not a major constrain for reaching relevant respiration levels in grape must. Indeed, only minor differences in ethanol yield were observed between the original and some of the recombinant strains. In contrast, some yeast strains showed a relevant reduction of acetic acid production. This was identified as a positive feature for the feasibility of alcohol level reduction by respiration. Reduced acetic acid production was confirmed by a thorough analysis of these and some additional deletion strains (involving genes HXK2, PYK1, REG1, PDE2 and PDC1). Some recombinant yeasts showed altered production of glycerol and pyruvate derived metabolites. Conclusions: REG1 and PDC1 deletion strains showed a strong reduction of acetic acid yield in aerobic fermentations. Since REG1 defective strains may be obtained by non-GMO approaches, these gene modifications show good promise to help reducing ethanol content in wines. [ABSTRACT FROM AUTHOR]

We have recently shown that ethanol yields in winemaking can be reduced by taking advantage of the respiratory metabolism of some non- Saccharomyces yeast species. Using an orthogonal design we have now addressed the impact of three environmental factors (temperature, nitrogen source, and oxygen supply level) on the aerobic metabolism in synthetic must of Saccharomyces cerevisiae , Metschnikowia pulcherrima , Kluyveromyces lactis , and Candida sake . An integrative parameter, Efficacy (efficacy for alcohol level reduction) was designed to simplify comparisons between strains or growth conditions. It integrates sugar consumption, ethanol yield, and acetic acid production data. We found a high relative impact of nitrogen source availability and temperature, as compared to aeration conditions, for several fermentation parameters, including ethanol yield. However, increasing oxygen supply showed a positive impact in terms of alcohol reduction and Efficacy for all the strains tested. The best results across assays were obtained for C. sake CBS 5093, with high sugar consumption rates, associated to low ethanol yields, and very low acetic acid production. Processes involving this yeast strain would benefit from high aeration levels and low nitrogen source availability; while fermentation temperatures would have little impact on its Efficacy for alcohol level reduction. [ABSTRACT FROM AUTHOR]

An approach consisting of controlling yeast inoculum to minimize volatile acidity production by Saccharomyces cerevisiae during the alcoholic fermentation of botrytized must was investigated. Direct inoculation of rehydrated active dry yeasts produced the most volatile acidity, while a yeast preparation pre-cultured for 24 hours reduced the final production by up to 23 %. Using yeasts collected from a fermenting wine as a starter must also reduced volatile acidity production. The conditions for preparing the inoculum affected the fermentation capacity of the first generation yeasts: fermentation duration, sugar to ethanol ratio, and wine composition. A pre-culture medium with a low sugar concentration (< 220 g/L) is essential to limit volatile acidity production in high sugar fermentations.

We have developed a wine fermentation procedure that takes advantage of the metabolic features of a previously characterized Metschnikowia pulcherrima strain in order to reduce ethanol production. It involves the use of M. pulcherrima/ Saccharomyces cerevisiae mixed cultures, controlled oxygenation conditions during the first 48 h of fermentation, and anaerobic conditions thereafter. The influence of different oxygenation regimes and initial inoculum composition on yeast physiology and final ethanol content was studied. The impact of oxygenation on yeast physiology goes beyond the first aerated step and influences yields and survival rates during the anaerobic stage. The activity of M. pulcherrima in mixed oxygenated cultures resulted in a clear reduction in ethanol yield, as compared to S. cerevisiae. Despite relatively low initial cell numbers, S. cerevisiae always predominated in mixed cultures by the end of the fermentation process. Strain replacement was faster under low oxygenation levels. M. pulcherrima confers an additional advantage in terms of dissolved oxygen, which drops to zero after a few hours of culture, even under highly aerated conditions, and this holds true for mixed cultures. Alcohol reduction values about 3.7 % ( v/ v) were obtained for mixed cultures under high aeration, but they were associated to unacceptable volatile acidity levels. In contrast, under optimized conditions, only 0.35 g/L acetic acid was produced, for an alcohol reduction of 2.2 % ( v/ v), and almost null dissolved oxygen during the process. [ABSTRACT FROM AUTHOR]

Performance of bulk freeze dried (BFD) cultures of dahi (D) and yoghurt (Y) either with or without probiotic cultures (AB - Lactobacillus acidophilus and Bifidobacterium bifidum) in standardized milk of cow and buffalo was evaluated. In buffalo milk, significantly ( p < 0.05) low viable count of probiotic culture combination of dahi cultures (DAB) over non probiotic combination (D) was noticed; whereas, difference in counts of yoghurt culture combinations Y and YAB was not significant. The culture activity of D and DAB was similar in both types of milk, however, the volatile acidity (VA) produced by combination D was higher (32.5 ml/50 g sample) in buffalo milk than in cow milk (29.2 ml/50 g sample). Whereas, DAB produced very low amount of VA (16 ml/50 g sample) both in cow and buffalo milk. The diacetyl and tyrosine contents produced by either D or DAB in cow or buffalo milk were in the same order. Although Y and YAB produced slightly more VA in buffalo milk than in cow milk, significant change in the performance of yoghurt cultures (Y or YAB) both in cow and buffalo milk was not noticed. However, the VA and acetaldehyde produced by YAB either in cow and buffalo milk was higher than that by combination Y. Addition of probiotic cultures significantly enhanced the production of acetaldehyde content in both types of milk. Difference in tyrosine content in yoghurt made either with cow or buffalo milk was not significant. Overall, the present study indicated that the BFD cultures can be used to prepare dahi or yoghurt either from cow or buffalo milk, without affecting the biochemical profile of these products. [ABSTRACT FROM AUTHOR]

The study refers to the possibilities and advantages of the alkalizing operation of the cocoa groats (roasted cocoa beans, crushed and peeled) and of the cocoa mass, mandatory operation in the cocoa powder technology and for the higher quality of chocolate. We presented the advantages and disadvantages of alkaline cocoa groats and cocoa mass, using data from the literature. We analyzed all of the cocoa groats alkalinity with the following alkali: potassium carbonate, concentrated ammonia and ammonium bicarbonate in different amounts. We determined that the decrease of the total acidity and volatile acidity compared to the control sample, indicating the alkaline substance with the most pronounced neutralizing effect. The same samples were determined using cocoa mass instead of cocoa groats and compared the results. It should be noted that by alkalizing we weren't expecting a complete neutralization of acids or acidic substances (as proof there are the residual acidity small values) because cocoa powder must present a slightly acid reaction (pH 6.97 to 6.98). If it is determined that the cocoa mass has final alkaline reaction, small amounts of citric acid or tartaric acid can be added, because the alkaline reaction impregnates an unpleasant leaching cocoa taste. The color of the cocoa powder is affected by three main factors, namely: the alkalinity, the fat content and the degree of tempering the powder during processing. Tempering the powder during processing can lead to a well expressed reddish brown, but can just as well lead to a pale pink and sometimes white or gray. If the tempering was done correctly during processing, it was found that the color of the powder depends on the fat content and the degree of alkylation. If the cocoa powder is more alkaline it is has a reddish hue and can even go to magenta. Magenta corresponds to the pH transition to alkaline environment, this change is accompanied by an unpleasant flavor. A moderate alkylation generally produce a pleasant and well expressed aroma, whereas excessive alkalinity can destroy almost completely the specific flavor. In practice, the basification must be controlled and driven in such a way as to achieve a favorable balance between the color and flavor. [ABSTRACT FROM AUTHOR]

Abstract: Respiration of sugars by non-Saccharomyces yeasts has been recently proposed for lowering alcohol levels in wine. Development of industrial fermentation processes based on such an approach requires, amongst other steps, the identification of yeast strains which are able to grow and respire under the relatively harsh conditions found in grape must. This work describes the characterization of a collection of non-Saccharomyces yeast strains in order to identify candidate yeast strains for this specific application. It involved the estimation of respiratory quotient (RQ) values under aerated conditions, at low pH and high sugar concentrations, calculation of yields of ethanol and other relevant metabolites, and characterization of growth responses to the main stress factors found during the first stages of alcoholic fermentation. Physiological features of some strains of Metschnikowia pulcherrima or two species of Kluyveromyces, suggest they are suitable for lowering ethanol yields by respiration. The unsuitability of Saccharomyces cerevisiae strains for this purpose was not due to ethanol yields (under aerated conditions they are low enough for a significant reduction in final ethanol content), but to the high acetic acid yields under these growth conditions. According to results from controlled aeration fermentations with one strain of M. pulcherrima, design of an aeration regime allowing for lowering ethanol yields though preserving grape must components from excessive oxidation, would be conceivable. [Copyright &y& Elsevier]

Several indigenous Saccharomyces strains from musts were isolated in the Jerez de la Frontera region, at the end of spontaneous fermentation, in order to select the most suitable autochthonous yeast starter, during the 2007 vintage. Five strains were chosen for their oenological abilities and fermentative kinetics to elaborate a Sherry base wine. The selected autochthonous strains were characterized by molecular methods: electrophoretic karyotype and random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and by physiological parameters: fermentative power, ethanol production, sugar consumption, acidity and volatile compound production, sensory quality, killer phenotype, desiccation, and sulphur dioxide tolerance. Laboratory- and pilot-scale fermentations were conducted with those autochthonous strains. One of them, named J4, was finally selected over all others for industrial fermentations. The J4 strain, which possesses exceptional fermentative properties and oenological qualities, prevails in industrial fermentations, and becomes the principal biological agent responsible for winemaking. Sherry base wine, industrially manufactured by means of the J4 strain, was analyzed, yielding, together with its sensory qualities, final average values of 0.9 g/l sugar content, 13.4 % (v/v) ethanol content and 0.26 g/l volatile acidity content; apart from a high acetaldehyde production, responsible for the distinctive aroma of 'Fino'. This base wine was selected for 'Fino' Sherry elaboration and so it was fortified; it is at present being subjected to biological aging by the so-called 'flor' yeasts. The 'flor' velum formed so far is very high quality. To the best of our knowledge, this is the first study covering from laboratory to industrial scale of characterization and selection of autochthonous starter intended for alcoholic fermentation in Sherry base wines. Since the 2010 vintage, the indigenous J4 strain is employed to industrially manufacture a homogeneous, exceptional Sherry base wine for 'Fino' Sherry production. [ABSTRACT FROM AUTHOR]

Abstract: Ultraviolet–visible irradiation was tested as an innovative technology that can help reducing the amount of sulfur dioxide used in white wine manufacturing. In addition, the effects of must freezing before processing were also investigated. Musts from Xarel·lo and Parellada varieties were vinified without any protective treatment, with a standard amount of SO2 addition or after an irradiation step. The results showed that UV–vis irradiation of must was able to prevent wine from spoilage in the same degree as SO2, without changing other quality parameters such as pH, tartaric acid and alcohol content. However, a residual addition of SO2 would be required in order to completely inhibit polyphenol oxidase activity. Moreover, the obtained changes in wine color parameters led to the conclusion that further optimization of the irradiation process is required before its implementation. Must freezing was shown to have some influence on quality parameters of Xarel·lo wines, but not in those from Parellada. [Copyright &y& Elsevier]

Acetic acid, a byproduct formed during yeast alcoholic fermentation, is the main component of volatile acidity (VA). When present in high concentrations in wine, acetic acid imparts an undesirable 'vinegary' character that results in a significant reduction in quality and sales. Previously, it has been shown that sake yeast strains resistant to the antifungal cerulenin produce significantly lower levels of VA. In this study, we used a classical mutagenesis method to isolate a series of cerulenin-resistant strains, derived from a commercial diploid wine yeast. Four of the selected strains showed a consistent low-VA production phenotype after small-scale fermentation of different white and red grape musts. Specific mutations in YAP1, a gene encoding a transcription factor required for oxidative stress tolerance, were found in three of the four low-VA strains. When integrated into the genome of a haploid wine strain, the mutated YAP1 alleles partially reproduced the low-VA production phenotype of the dip-loid cerulenin-resistant strains, suggesting that YAP1 might play a role in (reg-ulating) acetic acid production during fermentation. This study offers prospects for the development of low-VA wine yeast starter strains that could assist winemakers in their effort to consistently produce wine to definable qual-ity specifications. [ABSTRACT FROM AUTHOR]

The fermented tea vinegar combines the beneficial properties of tea and vinegar. The complete fermentation takes 4 to 5 weeks in a batch culture and thus can be shortened by semi continuous/ continuous fermentation using immobilized bacterial cells. In the present study, alcoholic fermentation of 1.0 and 1.5% tea infusions using Saccharomyces cerevisae G was carried out that resulted in 84.3 and 84.8% fermentation efficiency (FE) respectively. The batch vinegar fermentation of these wines with Acetobacter aceti NRRL 746 at the initial 1% acidity yielded 4.5 and 4.7% volatile acidity with 71.4 and 73% FE in 24 days. The semi continuous fermentation using sugarcane bagasse adsorbeded A.aceti cells produced 4.4% of volatile acidity from 1.5% tea wine (8.9% ethanol and 1.0% acidity), in 9 flow cycles, each of 4 h duration in a fermentation column at 50 ml/h. In the scale up process, 600 ml 1.5% tea wine produced 4.3% volatile acidity at 42.7% FE in 9 flow cycles of 12 h duration each. [ABSTRACT FROM AUTHOR]

etic acid is the main component of the volatile acidity of grape musts and wines. It can be formed as a by-product of alcoholic fermentation or as a product of the metabolism of acetic and lactic acid bacteria, which can metabolize residual sugars to increase volatile acidity. Acetic acid has a negative impact on yeast fermentative performance and affects the quality of certain types of wine when present above a given concentration. In this mini-review, we present an overview of fermentation conditions and grape-must composition favoring acetic acid formation, as well the metabolic pathways leading to its formation and degradation by yeast. The negative effect of acetic acid on the fermentative performance of Saccharomyces cerevisiae will also be covered, including its role as a physiological inducer of apoptosis. Finally, currently available wine deacidification processes and new proposed solutions based on zymological deacidification by select S. cerevisiae strains will be discussed. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we evaluate the applicability of previously characterized commercial and indigenous Saccharomyces cerevisiae strains and non-S. cerevisiae species for the deacidification of white and red wines at a pilot scale. The effect of the refermentation process (mixture of acidic wine with musts from freshly crushed grapes or with residual marc) as well as micro-oxygenation (MO) on acetic acid removal efficiency and wine aromatic composition was also assessed in a red wine. The commercial strains S26 and S29 efficiently reduced both acetic acid (43 and 47%, respectively) and sugar (100%) after 264h of refermentation of an acidic white wine that was supplemented with grape must. Similar results (60–66% of acetic acid removal) were observed for red wine deacidification using grape must, independently of MO. When residual marc was used for deacidification, strain S26 removed 40% of acetic acid, whereas strain S29 did not initiate refermentation with or without MO. Wines obtained by refermentation with the must had significantly lower acetic acid and a higher total SO2 concentration in comparison to the wines deacidified by the grape marcs. The volatile aroma compound''s composition of deacidified red wines was dependent on the refermentation process used, rather than on MO. The marc-deacidified wine obtained by the use of strain S26 and without MO achieved the best sensory classification. When data from all analytical and sensory evaluation were combined, Principal Component Analysis (PCA) separated the wines into three distinct groups according to the strain and the refermentation process independently of MO. We successfully established an efficient and cheap enological solution for the rectification of volatile acidity of wines. [Copyright &y& Elsevier]

Abstract: In this study, several strains of Torulaspora delbrueckii yeast species were evaluated in the laboratory for their enological properties. In a preliminary step, the ability of different molecular methods to discriminate among T. delbrueckii strains was compared. A combination of 7 PCR methods was able to separate 21 strains into 18 groups, while an REA-PFGE method allowed, in one experiment, the separation into 19 groups. The T. delbrueckii strains used presented a wide phenotypic variability in fermentation behaviour, e.g. Lag Phase (LP) duration, T50 parameter (time necessary to ferment half the sugar), and ethanol production. These 3 parameters have to be considered for industrial selection, particularly the LP duration. The majority of T. delbrueckii strains produced 8 to 11% and 7 to 10% ethanol vol. at 17°C and 24°C, respectively, with a maximum ethanol concentration of 12.35 at 17°C and 10.90% vol. at 24°C. The phenotypic variability of this species was also reflected in volatile acidity, glycerol, and aroma production. These experiments confirmed the low volatile acidity and glycerol production of this species and revealed a difference in osmotic stress response, compared to Saccharomyces cerevisiae. T. delbrueckii presented high fermentation purity and produced low levels of undesirable volatile compounds, such as hydrogen sulphide and volatile phenols. [Copyright &y& Elsevier]

Abstract: The effects of nitrogen addition into nitrogen deficient/depleted media on the release of aroma compounds post-fermentation were investigated in three commercial yeast strains of Saccharomyces cerevisiae which highlight the yeast strain effect as well as nitrogen effects. By comparing the two timings of nitrogen addition, prior to fermentation or later at stationary phase (72 h), it was shown that nitrogen addition at stationary phase significantly decreases ethanol and acetic acid formation and significantly increases the following compounds: 2-phenylethanol, ethyl isobutyrate, 2-phenylethyl acetate, ethyl 2-methylbutyrate and ethyl propionate in the three strains, and also isovaleric acid, isoamyl alcohol and ethyl isovalerate in both PYCC4072 and UCD522. The strain EC1118 produced significantly less medium chain fatty acids, hexanoic, octanoic and decanoic acids and their respective esters after nitrogen addition. Therefore, timing of nitrogen addition to a ferment media can vary the concentration of certain aroma compound and might provide a means for varying wine composition. [Copyright &y& Elsevier]

Aerobic fermentation was previously proposed to reduce the ethanol content of wine. The main constraint found for Saccharomyces cerevisiae to be used under these conditions was the high levels of acetic acid produced by all S. cerevisiae strains previously tested. This work addressed the identification of S. cerevisiae wine yeast strains suitable for aerobic fermentation and the optimization of fermentation conditions to obtain a reduced ethanol yield with acceptable volatile acidity. This approach unveiled a great diversity in acetic acid yield for different S. cerevisiae strains under aerobic conditions, with some strains showing very low volatile acidity. Three strains were selected for further characterization in bioreactors, with natural grape must, under aerobic and anaerobic conditions. Ethanol yields were lower under aerobic than under anaerobic conditions for all strains, and acetic acid levels were low for two of them. Strain-dependent changes in volatile compounds were also observed between aerobic and anaerobic conditions. Finally, the process was optimized at laboratory scale for one strain. This is the first report of S. cerevisiae wine strains showing low acetic acid production under aerobic conditions and paves the way for simplified aerobic fermentation protocols aimed to reducing the alcohol content of wines. [Display omitted] • Great diversity in acetate yield for S. cerevisiae strains under aerobic conditions. • Strains with low acetate yield can be useful for winemaking under aerobic conditions. • Changes in volatile compound profile between aerobic and anaerobic conditions. • Profile of volatile compounds under aerobic conditions differs between strains. • A gradual decrease of oxygen availability helps to keep acetic acid levels low. [ABSTRACT FROM AUTHOR]

Herein, we isolate and characterize wine yeasts with the ability to reduce volatile acidity of wines using a refermentation process, which consists in mixing the acidic wine with freshly crushed grapes or musts or, alternatively, in the incubation with the residual marc. From a set of 135 yeast isolates, four strains revealed the ability to use glucose and acetic acid simultaneously. Three of them were identified as Saccharomyces cerevisiae and one as Lachancea thermotolerans. Among nine commercial S. cerevisiae strains, strains S26, S29, and S30 display similar glucose and acetic acid initial simultaneous consumption pattern and were assessed in refermentation assays. In a medium containing an acidic wine with high glucose–low ethanol concentrations, under low oxygen availability, strain S29 is the most efficient one, whereas L. thermotolerans 44C is able to decrease significantly acetic acid similar to the control strain Zygosaccharomyces bailii ISA 1307 but only under aerobic conditions. Conversely, for low glucose–high ethanol concentrations, under aerobic conditions, S26 is the most efficient acid-degrading strain, while under limited-aerobic conditions, all the S. cerevisiae strains studied display acetic acid degradation efficiencies identical to Z. bailii. Moreover, S26 strain also reveals capacity to decrease volatile acidity of wines. Together, the S. cerevisiae strains characterized herein appear promising for the oenological removal of volatile acidity of acidic wines. [ABSTRACT FROM AUTHOR]

Abstract: Conventional wine yeasts produce high concentrations of volatile acidity, mainly acetic acid, during high-sugar fermentation. This alcoholic fermentation by-product is highly detrimental to wine quality and, in some cases, levels may even exceed legal limits. In this study, a non-conventional species, Torulaspora delbrueckii, was used, in pure cultures and mixed with Saccharomyces cerevisiae yeast, to ferment botrytized musts. Fermentation rate, biomass growth, and the formation of volatile acidity, acetaldehyde, and glycerol were considered. This study demonstrated that T. delbrueckii, often described as a low acetic producer under standard conditions, retained this quality even in a high-sugar medium. Unlike S. cerevisiae, this species did not respond to the hyper-osmotic medium by increasing acetic production as soon as it is inoculated into the must. Nevertheless, this yeast produced low ethanol and biomass yields, and the fermentation was sluggish. As a result, T. delbrueckii fermentations do not reach the required ethanol content (14%vol.), although this species can survive at this concentration. A mixed culture of T. delbrueckii and S. cerevisiae was the best combination for improving the analytical profile of sweet wine, particularly volatile acidity and acetaldehyde production. A mixed T. delbrueckii/S. cerevisiae culture at a 20:1 ratio produced 53% less in volatile acidity and 60% less acetaldehyde than a pure culture of S. cerevisiae. Inoculating S. cerevisiae after 5 days'' fermentation by T. delbrueckii had less effect on volatile acidity and acetaldehyde production and resulted in stuck fermentation. These results contribute to a better understanding of the behaviour of non-Saccharomyces and their potential application in wine industry. [Copyright &y& Elsevier]

Aims: The objective of this study was to determine the effect of increasing juice soluble solids above 40°Brix on wine yeast’s ability to grow and ferment the juice, with particular focus on acetic acid production, titratable acidity (TA) changes and the maximum amount of sugar consumed by the yeast. Methods and Results: Riesling Icewine juices at 40, 42, 44 and 46°Brix were inoculated with K1-V1116 at 0·5 g l−1 and fermented at 17°C until sugar consumption ceased. Increasing soluble solids showed strong negative linear correlations with yeast growth, sugar consumption and ethanol production ( r = −0·999, −0·997 and −0·984, P < 0·001, respectively). Acetic acid, glycerol and TA production normalized to sugar consumed showed strong positive correlations to the initial juice concentration ( r = 0·992, 0·963 and 0·937, P < 0·001, respectively) but no correlation was found for ethanol production. The acetic acid produced as a function of sugar consumed was positively correlated to the glycerol produced ( r = 0·970, P < 0·001). The final TA of the wines ranged between 11·8 and 13·7 g l−1 tartaric acid, increasing by 2·3–3 g l−1 over the starting juice. The increase in TA was positively correlated to the increase in acetic acid produced after normalizing the data to the amount of sugar consumed ( r = 0·975, P < 0·001). The acid equivalents resulting from the increase in acetic acid accounted for 80–100% of the TA increase when converted to units of tartaric acid. In the final Icewines, acetic acid represented 19–20% of wine TA. Conclusions: Increasing Icewine juice concentration from 40 to 46°Brix increases the proportion of yeast sugar metabolism towards glycerol and acetic acid production to cope with the increased osmotic stress by decreasing yeast growth, sugar consumption rate, the total amount of sugar consumed and the total amount of ethanol produced. The high proportional contribution of acetic acid to titratable acidity in Riesling Icewine may affect acidity perception. Significance and Impact of the Study: We have determined that 10% v/v ethanol would not be achievable with initial juice concentrations above 42° Brix and that Riesling Icewine juice above 52·5°Brix would be theoretically unfermentable. The high proportional contribution of acetic acid to TA may be an important factor in the organoleptic balance of these Icewines. [ABSTRACT FROM AUTHOR]

The present study investigated chemical and sensory properties of Malvasia delle Lipari DOC (Denomination of Controlled Origin) wine fermented with a crytolerant strain of Saccharomyces uvarum, characterized by low levels of acetic acid production. In particular, experimental wine was tested for volatile acidity and for aromatic profile by gas chromatography and the results were compared with the same wine produced with a commercial strain of Saccharomyces cerevisiae. Sensory analysis was carried out to assess the identification of experimental wine as Malvasia delle Lipari by defining its sensory profile. Fermentation with S. uvarum gave a final product with lower volatile acidity, lower alcohol content and higher total acidity. Moreover, differences in the aroma profile could be ascribed to different characteristics of the yeasts. Concerning sensorial analysis, the panel assigned higher scores in positive attributes to the wine fermented with S. uvarum [ABSTRACT FROM AUTHOR]

We analyzed the variability of volatile acidity and glycerol production by Saccharomyces cerevisiae on a large sample of high sugar musts. The production of volatile acidity was inversely correlated with the maximum cell population and the assimilable nitrogen concentration. The higher the nitrogen concentration, the less volatile acidity was produced. An approach to minimize volatile acidity production during high sugar fermentations by adjustment of assimilable nitrogen in musts was investigated in terms of both quantity and addition time. It was found that the optimal nitrogen concentration in the must is 190 mgN·l−1. The best moment for nitrogen addition was at the beginning of fermentation. Addition at the end of the growth phase had less effect on volatile acidity reduction. We suggest that by stimulating cell growth, nitrogen addition provides NADH in the redox-equilibrating process, which in turn reduces volatile acidity formation. [Copyright &y& Elsevier]

Off-flavors produced by undesirable microbial spoilage are a major concern in wineries, as they affect wine quality. This situation is worse in warm areas affected by global warming because of the resulting higher pHs in wines. Natural biotechnologies can aid in effectively controlling these processes, while reducing the use of chemical preservatives such as SO2. Bioacidification reduces the development of spoilage yeasts and bacteria, but also increases the amount of molecular SO2, which allows for lower total levels. The use of non-Saccharomyces yeasts, such as Lachancea thermotolerans, results in effective acidification through the production of lactic acid from sugars. Furthermore, high lactic acid contents (>4 g/L) inhibit lactic acid bacteria and have some effect on Brettanomyces. Additionally, the use of yeasts with hydroxycinnamate decarboxylase (HCDC) activity can be useful to promote the fermentative formation of stable vinylphenolic pyranoanthocyanins, reducing the amount of ethylphenol precursors. This biotechnology increases the amount of stable pigments and simultaneously prevents the formation of high contents of ethylphenols, even when the wine is contaminated by Brettanomyces. [ABSTRACT FROM AUTHOR]